Physical modelling was performed to study the hydrodynamics and wake interferences of a tidal stream turbine sited in close proximity to different seabed elements. The seabed topography variation had a significant effect on the tidal stream turbine behavior. The average power output of the turbine with the presence of the small seabed topography increased by about 11%, while the power output of the turbine sited in close proximity to the larger seabed topography was reduced by approximately 40% compared to that with a flat bed. Additionally, detailed flow field measurements of the turbine wake revealed the seabed topography variation effects on the wake characteristics. The small seabed topography increased the average turbulence intensity in the near wake region behind the turbine and made the flow velocity recovery slightly faster than the case with flat bed. In contrast to the small seabed topography, the larger topography had a certain inhibitory effect on wake recovery. The results presented in the current study not only offer a validation database for wake models but can also be used to optimize the site selection and rotor placement of tidal turbines for a higher power yield.